Meegan Larsen

Animal Health Laboratory, University of Guelph, Guelph, ON.

AHL Newsletter 2026;30(2):8.

A clinically healthy, first lactation heifer aborted at approximately 200 days in calf. Multiple late term abortions had occurred on the farm over the previous 6 months. The fetus and a small piece of placenta, including two cotyledons, were submitted to the AHL for postmortem examination. The skin of the eyelid of the fetus was roughened and there was thickening of the intercotylendonary placenta. The most significant microscopic finding was a necrotizing placentitis with numerous intralesional fungal hyphae (Fig. 1). The roughened fetal eyelid skin corresponded to an area of epidermal hyperkeratosis with intracorneal pustules (Fig. 2). Eyelid pustules are often a feature of mycotic placentitis; however, no hyphae were observed in this case. There was also a mild suppurative and histiocytic fetal pneumonia. Collectively, the histologic lesions were diagnostic for mycotic abortion, and this diagnosis was confirmed by the visualization of fungal hyphae on a placental wet mount. No concurrent bacterial or viral causes of abortion were identified via bacterial culture or PCR testing.

Mycotic abortion in cows is generally caused by Aspergillus fumigatus or Mucor species of fungi. It occurs due to ingestion or inhalation of spores from moldy feed or bedding, followed by hematogenous spread to the uterus and placenta. This infection is associated with sporadic, usually mid-late term abortions in a herd. The incidence is highest between November and April, likely due to confinement and high-density housing over the winter. The dam often does not show signs of illness prior to or after the abortion, but retained placenta is relatively common.

Figure 1. Placental necrosis with numerous fungal hyphae stained black. GMS stain.

Figure 2. Excess lamellar keratin on the epidermal surface of the eyelid (*) with a pustule (arrow).